Safe to use module resolution if new file is created

Author: sheetalkamat

src/compiler/program.ts

@@ -1374,7 +1374,7 @@ namespace ts {
                     : host.getSourceFile(oldSourceFile.fileName, options.target!, /*onError*/ undefined, shouldCreateNewSourceFile); // TODO: GH#18217
 
                 if (!newSourceFile) {
-                    return StructureIsReused.Not;
+                    return StructureIsReused.SafeModules;
                 }
 
                 Debug.assert(!newSourceFile.redirectInfo, "Host should not return a redirect source file from `getSourceFile`");

tests/baselines/reference/tscWatch/programUpdates/deleted-files-affect-project-structure-2.js

@@ -122,7 +122,7 @@ Output::
 
 Program root files: ["/a/b/f1.ts","/a/c/f3.ts"]
 Program options: {"watch":true,"noImplicitAny":true}
-Program structureReused: Not
+Program structureReused: SafeModules
 Program files::
 /a/lib/lib.d.ts
 /a/b/f1.ts

tests/baselines/reference/tscWatch/programUpdates/deleted-files-affect-project-structure.js

@@ -122,7 +122,7 @@ Output::
 
 Program root files: ["/a/b/f1.ts"]
 Program options: {"watch":true,"noImplicitAny":true}
-Program structureReused: Not
+Program structureReused: SafeModules
 Program files::
 /a/lib/lib.d.ts
 /a/b/f1.ts

tests/baselines/reference/tscWatch/programUpdates/rename-a-module-file-and-rename-back-should-restore-the-states-for-inferred-projects.js

@@ -96,7 +96,7 @@ Output::
 
 Program root files: ["/a/b/file1.ts"]
 Program options: {"watch":true}
-Program structureReused: Not
+Program structureReused: SafeModules
 Program files::
 /a/lib/lib.d.ts
 /a/b/file1.ts

tests/baselines/reference/tscWatch/watchEnvironment/watchDirectories/with-non-synchronous-watch-directory-renaming-a-file.js

@@ -132,7 +132,7 @@ Output::
 
 Program root files: ["/user/username/projects/myproject/src/file1.ts","/user/username/projects/myproject/src/file2.ts"]
 Program options: {"outDir":"/user/username/projects/myproject/dist","watch":true,"project":"/user/username/projects/myproject/tsconfig.json","configFilePath":"/user/username/projects/myproject/tsconfig.json"}
-Program structureReused: Not
+Program structureReused: SafeModules
 Program files::
 /a/lib/lib.d.ts
 /user/username/projects/myproject/src/file1.ts

tests/baselines/reference/tscWatch/watchEnvironment/watchDirectories/with-non-synchronous-watch-directory.js

@@ -129,7 +129,7 @@ Output::
 
 Program root files: ["/user/username/projects/myproject/src/file1.ts"]
 Program options: {"watch":true,"project":"/user/username/projects/myproject/tsconfig.json","configFilePath":"/user/username/projects/myproject/tsconfig.json"}
-Program structureReused: Not
+Program structureReused: SafeModules
 Program files::
 /a/lib/lib.d.ts
 /user/username/projects/myproject/src/file1.ts